Crystal Palace continued their recent revival to boost their Premier League survival hopes and leave Arsenal struggling to maintain their run of top-four finishes under Arsene Wenger.
Palace led through Andros Townsend's close-range finish, doubling their lead when Yohan Cabaye's shot looped in.
Luka Milivojevic clinched victory with a firm, low penalty as Palace moved six points clear of the relegation zone.Sixth-placed Arsenal did not manage a shot on target in a poor second half.
Some travelling Gunners fans again called for manager Wenger, who has led Arsenal to top-four finishes in each of his previous 20 seasons at the helm, to leave the club.
The Frenchman's side are seven points adrift of fourth-placed Manchester City with eight games remaining.
Feeble Arsenal put more heat on Wenger
The manner of Arsenal's performance - disorganised, devoid of attacking ideas and lacking fight - will increase the scrutiny on Wenger yet again.
The 67-year-old has already faced protests from some supporters urging him to leave, with more calls clearly audible - along with the barracking of his players in the latter stages - at Selhurst Park.
Wenger's contract expires at the end of the season and the club has offered him a new two-year deal, although he is still to announce whether he intends to carry on.
Arsenal had 72% possession against Palace but that mattered for little as the hosts broke quickly on the counter-attack, exploiting space down the flanks and taking their chances clinically.
The Gunners looked defensively vulnerable whenever Palace went forward, lacking leadership without injured captain Laurent Koscielny.
And when the visitors did attack, Palace keeper Wayne Hennessey was only required to make saves from Mohamed Elneny and Alexis Sanchez.
After the break, Hennessey did not even face a shot on target as Arsenal suffered a fourth straight away defeat for the first time under Wenger.
"Palace wanted it more. You could sense that from the kick-off," Theo Walcott, Arsenal's stand-in captain, said.
Big Sam to avoid relegation again?
While Wenger has never led Arsenal to a finish outside the top four, opposite number Sam Allardyce has a proud record of not being relegated from the top flight.
On this evidence, Allardyce looks much likelier to maintain his achievement than his long-time adversary.
The former England manager, who has previously kept up Bolton, Blackburn and Sunderland, took a while to improve Palace's fortunes after replacing Alan Pardew in December, but the Eagles are starting to reap the rewards of his methods when it matters.
Palace had too much pace, power and passion for a lifeless Gunners side.
Although Arsenal dominated possession in the first half, Palace had the better chances and deservedly led when Townsend drilled in Wilfried Zaha's cross from the right.
Palace leaked goals under Pardew, but have discovered defensive resilience under Allardyce - leading to four clean sheets in their past six league games.
That run has coincided with the arrival of centre-back Mamadou Sakho, the loan signing from Liverpool who again led their backline with a determined and disciplined performance.
It laid the platform for Palace to go on and secure victory after the break.
Cabaye clipped Zaha's pass into the top corner before Gunners keeper Emiliano Martinez clumsily brought down Townsend, allowing Milivojevic to confidently tuck in his first Palace goal.
"Tactically the players were aware of what had to happen to beat Arsenal," said Allardyce.
"Arsenal have been weak defensively - they leave the centre-backs exposed."
Man of the match - Andros Townsend (CrWhat the managers said
Crystal Palace manager Sam Allardyce, speaking to Sky Sports: "Tactically the players were aware of how to beat Arsenal. The first thing was to defend and frustrate them, keep them playing sideways, then use the space behind the full-backs. Arsenal have been weak defensively, they leave the centre-backs exposed.
"We won a lot of possession off them and created lots of chances. Cabaye's goal, what a finish - and that was down to us pressing them. It wasn't a shock for me because we played Chelsea and won that game. The result might be a shock, but we did that again and did it better.
"We all know Arsenal are going through their worst spell for years, but the only way to take advantage is by playing well. Everything worked perfectly for us today."CrystaArsenal manager Arsene Wenger, speaking to BBC Sport: "We lost too many duels and we paid for that. There is no obvious reason why. We prepared well. It's difficult to explain just after the game.
"I don't think my players didn't want it, but we lost duels in decisive moments and that's how games are decided at this level.
"I understand our fans are disappointed and we all are deeply tonight. It's very worrying and disappointing the way we lost the game. Palace were sharp, they beat Chelsea the other day, and that shows they have quality.
"We are in a difficult position. The game doesn't help."
